This invention relates to the field of drilling.
More particularly, the invention concerns a device for controlling the orientation of bore holes.
In many instances, particularly in mining operations, it is highly desirable and sometimes vital, to be able to drive a bore hole as close as possible to the intended spot. For example, this is evidently desirable when the bore hole is being driven to gain access to a new underground area of coal or another substance to be mined. On the other hand, the ability to be able to drive a bore hole directly to a chosen spot may become a matter of life and death if one or more workers are trapped underground and the bore hole is being driven to either supply them with air, food and/or medicine, or else to physically remove them to safety through the bore hole.
The problem with the prior art is that it is not effective.
It is known to incorporate in the drill string a rigid guide rod which is located behind the drill bit and is intended to stabilize the drill string, which it does in fact do. Such guide rods cannot, however, prevent a deviation of the bore hole from its intended path, as it occurs during the course of drilling. Even less, of course, can these rods correct such a deviation once it occurs. And finally, if a deviation does occur no one will know of its details until the drill target is or should be reached and it is found that the bore hole does not come out where intended.
A proposal has been made to provide these guide rods with pendulum controls to cause them to more or less automatically maintain the bore hole "on target". Such controls are, however, quite complicated and expensive. Moreover, they are susceptible to malfunctions due to errors in setting or operating malfunctions in the control itself. This will then again lead to borehole deviations which can be detected only when the drilling operation is completed and it is discovered that the bore hole does not come out where intended. Also, these controls have a certain inertia factor which in itself may give rise to bore hole deviations.